The layers of a typical magnetic disk may include an underlayer of chrome, one or more magnetic layers for information storage and a carbon overcoat. The layers are formed in succession on a suitable substrate. Different layers may be formed in different chambers of a multiple chamber sputter coating system. Sputter coating systems of this type are disclosed, for example, in U.S. Pat. No. 5,215,420 issued Jun. 1, 1993 to Hughes et al and are commercially available from Intevac Inc. of Santa Clara, Calif.
Magnetic disks are conventionally fabricated on metallic substrates. During formation of the layers on the substrate, a bias voltage may be applied to the metallic substrate. Ions within the processing chamber are accelerated toward the substrate by the bias voltage. Depending on the particular process, the acceleration of ions toward the substrate may increase the deposition rate in comparison with an unbiased substrate, may modify the disk surface by ion bombardment, and may produce other desirable effects. In the case of a metallic substrate, the bias voltage may be applied to the substrate through the fingers that physically hold the disk in position for processing.
It has become desirable to use insulating substrates in some applications. For example, glass substrates may be utilized in the fabrication of magnetic disks for laptop computers because of their light weight and durability. However, a problem arises in the processing of glass substrates, because the glass substrate cannot be biased by application of a voltage. Accordingly, the processes utilized with metallic substrates cannot be applied directly to glass substrates. For this reason, processing of glass substrates may be slower than processing of metallic substrates, resulting in higher costs, and the properties of the layers formed on glass substrates may differ from those of the layers formed on metallic substrates.
Accordingly, there is a need for improved methods and apparatus for processing insulating substrates, such as glass substrates.